The aim of this proposal is to study several well-defined systems in which proteins and lipids interact. Such interaction are essential to the assembly and function of biological membranes. The systems are i) the action of the bacterial enzyme cyclopropane fatty acid synthase, ii) morphogenesis of the lipid-containing bacteriophage PR4, and iii) isolation of mutants of the yeast, Saccharomyces cereviseae, deficient in phospholipid exchange proteins. Cyclopropane fatty acid synthase is the only discrete enzyme known to specifically react with the nonpolar portion of a phospholipid bilayer. We propose to prepare large quantities of this enzyme by recombinant DNA techniques and to study its detailed interaction with its phospholipid substrate. Phage PR4 acquires its capsid lipid from the bacterial membrane and this process seems a good model to study membrane morphogenesis by genetic means. We propose to use a combination of genetics and biochemistry to study the mechanisms whereby the phage lipids are incorporated. Lipid exchange proteins are ubiquitous in nature and a number of mammalian proteins have been purified and studied. However, the function of these proteins is unknown. S. cereviseae has such proteins, is a typical eucaryote, and has a sophisticated genetic system. We propose to exploit this genetic system to isolate mutants difficient in these proteins. Such mutants will allow deduction of the role of these proteins in eucaryotic cells. Proper function and formation of biological membranes is essential for cell viability. These projects should provide much needed information on the mechanism of membrane morphogenesis and function. A large number of disease processes are associated with defects in membrane morphogenesis.